Solvent extraction of hydrocarbon oil



June 23, 1936.

L. A. CLARKE som/ENTl EXTRAGTION oF HYDRocARBoN OIL Filed'April 19,- '1932 Pump TRHTED METHYL ICETAVTA' IETHYL pOLA-f? INVENTOR BY @MM H/s ATTORNEY Patented June 23, 1936 UNITED STATES SOLVENT EXTRACTION 0F HYDRO- GARBON OIL Louis A. Clarke, Fishkill, N. Y., assigner to The Texas Company, New York, N. Y., a corporation of Delaware Application April 19, 1932, Serial No. 606,110

5 Claims.

This invention relates to a process for extracting hydrocarbon lubricating oils with a selective solvent, and more particularly relates to a process of effecting the removal of those hydrocarbons which tend to lower the viscosity index of a hydrocarbon lubricating oil. The invention is directed especially to the process of extracting hydrocarbon lubricating oils with methyl acetate.

It has been found that the hydrocarbons which tend to lower the viscosity index of a hydrocarbon lubricating oil are soluble in methyl acetate, and by extracting the oil with methyl acetate these hydrocarbons may be removed by the solvent and separated from the remaining oil, thereby producing a lubricating oil having a. high viscosity index, a low sulphur content, and having extreme resistance to oxidation; such refined oils are also characterized by showing low carbon residue when tested according to the Con-y radson method.`

The invention also contemplates continuously and countercurrently extracting lubricating oil with the solvent, methyl acetate.

It is well known that petroleum products generally contain four groups or types of hydrocarbons, namely, paraflns, naphthenes, aromatics and unsaturates. Of these, the paraflins are the least reactive and the aromatics and unsaturates the most reactive, the naphthenes occupying intermediate positions in the ascending order of reactivity.

This ascending order of reactivity is believed also to be paralleled by the degrees of polarity of the four enumerated types of hydrocarbons. The paraflins are considered to be strictly nonpolar while naphthenes, aromatics and unsaturates are polar. It has been demonstrated that the paraiiins or non-polar hydrocarbons are characterized by having high viscosity indices while the polar bodies which may include the naphthenes, aromatics and unsaturates have low viscosity indices. It is known that the solubilities in polar solvents of the four groups of hydrocarbons Vary directly as their reactivities and their polarities, with the paraffms being the least soluble and the aromatics and unsaturates the most soluble.

Prior to my invention, it was thought that extremely polar solvents, among which may be enumerated sulphur dioxide, liquid ammonia and (Cl. 196-I3) liquid carbon dioxide, were necessary for the extensive extractions which must be made in order to permit of the isolation of the paraffin hydrocarbons. Of these solvents, sulphur dioxide has most. commonly found favor.v Its application, however,` has certain drawbacks. Sulphur dioxide is under normal conditions a gaseous material and in order to bring it into the liquid form and to maintain it in that condition, low temperatures and high pressuresv are necessary. Installations for extracting hydro-carbon oils with liquid sul.- phur dioxide therefore involve costly apparatus for* liquefyng the solvent, high pressure vessels for carrying out the extractions at low temperatures and complex distillation equipment for liberating and recovering the sulphur dioxide dissolved in the products of the extraction.

Now I have found that methyl acetate, which is a liquid under normal conditions of` temperature and pressure, may be used for the extraction of polar hydrocarbons from hydrocarbon mixtures which function it performs much more eiiiciently and successfully than even sulphur dioxide. I have applied this characteristic of methyl acetate to the preparation of lubricating oils which after treatment therewith are substantially parailinic in character and which are characterized by their high viscosity indices, are low in. sulphur, resistant to oxidation-and yield low Conradson carboni residues. The extraction with methyl acetate may be carriedv out at normal temperatures and pressures; this is a distinct ad.- vantage. Complex equipment and solvent purifying systems are not necessary in its application. Its chemical stability is of such a high order that special materials are not necessary in the construction of the apparatus in which it is used. Its boiling point of 57.5 C. is of such a low order of magnitude as to permit its ready separation from both the extracted oil. and from the extract which it has dissolved fromv the oil.. It is not, however, so volatile as to necessitate a special vapor recovery system. Experience has shown that by using a closed system, the solvent loss by this method of rening is exceedingly small.

For a better understanding ofr my invention, reference may be had to the accompanying drawing which sets forth a flow sheet of a countercurrent treating system which may be used with advantage in the application of my invention.

The numeral 9 indicates a storage tank for unextracted oil. This is connected by line II which is fitted with a contro1 valve IIJ, to a mixing chamber I2 wherein the unextracted oilis agitated with partly spent methyl acetate from a subsequent extraction step. This chamber is in turn connected by line I3 with a settling chamber I4 which may advantageously be of greater diameter than the mixing chamber. Herein the mixture of partly extracted oil and completely spent methyl acetate having in solution low viscosity index or polar bodies separated from the oil is allowed to stratify. The partly extracted oil is drawn off from an upper point in the settling chamber I4 through line I6, which is controlled by valve I5, and is introthrough the line I9 which in turn is controlled,

by valve 20. The mixture of extracted oil and partly spent methyl acetate having in solution further quantities of polar bodies extracted fromY the oil is then passed through line 22 into settling chamber 23. This settling chamber is similar in construction to settling chamber I4. Stratication of the mixture is allowed to take place in this vessel, the supernatant extracted oil containing in solution a small amount of methyl acetate being drawn 01T through line 25 which is controlled by valve 24. The partly spent methyl acetate containing in solution polar bodies is passed through line 26 controlled by valve '21 into mixing chamber I2.

The treated oil containing in solution a small quantity of methyl acetate is then circulated by means of pump 28 through the coils 29 of the heater` 30. The oil having been heated is discharged from the heater 30 and isthen permitted to expand through valve,32 into a flash tower 33, wherein substantially all of the solvent is distilled. oi from the treated oil. The vapors of methyl acetate pass out through line 34 fitted with valve35 which connects the uppermost point in the tower 33 to the inlet 54 of the condenser coils 55. nected by line 31 controlled by valve 36 with a cooler 38 from which the cool treated oil is drawn off through line 39 into the treated oil storage tank 4l).

The completely spent methyl acetate having in solution the polar or low viscosity index bodies extracted from the treated oil is drawn off from the bottom of settling chamber I4 through line I8 controlled by valve I1 and passes to the suction side of pump 4I. This pump circulates the solution of low viscosity index bodies in methyl acetate through the coils 42 of heater 43 from which it passes through line 44 to expansion valve 45 where it is expanded into flash tower 46. The evolved vapors of methyl acetate are drawn oi from the top of tower 46 through line 41 controlled by valve 48 into the inlet 54 ofcondenser coils 55. The bottom of the tower 46 tate i,S drawn. Qtr.. through 1.111958; csntrqlled. br.

The bottom of tower 33 is con-` valve 51 into the methyl acetate storage tank 59.

In the preferred manner of practicing the invention with the apparatus illustrated in the drawing, a suitable lubricating oil of low viscosity index and which may have been subjected to treatment with sulphuric acid is passed into the mixing chamber I2 at a temperature of approximately '10 F. wherein it is thoroughly agitated with partly spent methyl acetate from a subsequent step in the treating operation. SimultaneouslyV an equal volume of methyl acetate is introduced at the other end of the treating circuit, namely, mixing chamber 2|. The unextracted parain. oil is agitated in mixing chamber I2 with partly spent methyl acetate from a subsequent step in the treating operation. The mixture of partly extracted oil and spent methyl acetate saturated with extract is then passed into settling chamber I4 wherein stratification of the oil and saturated methyl acetate is allowed to take place. The supernatant partly extracted oil is then passed into mixing chamber 2I wherein it is agitated with fresh methyl acetate, the volume of which is equal to the volume of unextracted oil.

The mixture of completely extracted oil and partly spent methyl acetate is then passed into the nal settling chamber 23 wherein stratification is allowed to take place. The lower layer of partly spent methyl acetate having in solution the polar or low viscosity index bodies from the treated oil is then passed to the aforementioned mixing chamber I2 while the supernatant treated oil, comprising aproximately 65% of the unextracted oil introduced into the system and containingv a small amount of methyl acetate in solution, is then pumped through the coils 29 of heater 30 wherein it is raised to a tempera-Y ture of approximately 220 Fgand a pressure of about 20 lbs. per square inch.

The extracted oil having in solution a small quantity of methylacetate is then expanded through valve 32 into stripping tower 33 to approximately atmospheric pressure which results in the vaporization of the methyl acetate. These vapors are passed out of the stripping tower through the vapor line 34 while the residual treated oil is drawn off from the bottom of the tower through line 31 to a cooler in which its temperature is reduced to approximately 90 F.

Concurrently, the spent methyl acetate having in solution a volume of low viscosity index bodies, approximately 35% of the original unextracted oil, is pumped through the coils 42 of heater 43 wherein the temperature is raised to 220 F. and to a pressure of approximately 25 lbs. per sq. in. It is then expanded through valve 45 into stripping tower 46 to a pressureof approximately atmospheric. 'I'he vapors of methyl acetate are drawn 01T through vapor line 41 while the extract which composes the bottoms 'is drawn off through line 50 into cooler 5I wherein the temperature is reduced to approximately F. The cooled extract is passed to extract storage tank 53.

The vapors of methyl acetate obtained lfrom stripping towers 33 and 46 are brought together into the inlet 54 of condenser coils 55 vwherein their temperature is reduced to 60 F. which ef. fects substantially complete condensation. The condensed methyl acetate is then drawn off throughY line 58 into methyl acetate storage tank A heavy red parain oil having the following tests Was submitted to extraction with methyl acetate whereby a quanty of low viscosity index bodies to the amount of 35% of the original unextracted oil was separated. 'Ihe tests of the treated or extracted oil as well as of the extract are given herewith:

Extlcted Extract Gravity A. P. I 30. 22.3 Flash, Cleveland open 455 F 445 F. Fire 525 F 495 F. Pour 55 F 20 F. Viscosity Saybolt universal at 100 F 271 472 130 134 200 Viscosity index... 108. 4 58. 0 Carbon residue- 0. 09 0. 55

It is to be understood that the gures quoted above serve merely to illustrate a typical operation of the process and accordingly may Vary. The constitution of the oil to be extracted as well as the characteristics and yield of the extracted oil desired, will determine the relative volumes of unextracted oil and methyl acetate introduced into the system as well as the temperatures necessary for stripping the methyl acetate from the extracted oil and from the extract.

In the foregoing specific example the extraction was carried out at a temperature of about 70 F. or normal room temperature and such temperatures are preferred in extracting with methyl acetate since high yields of high viscosity index oil may be secured. However, other temperatures of extraction may be employed ranging from above the pour point of the oil being treated to about 130 F. depending upon the character of oil and the extent of extraction required. Obviously, the temperature in any event should be sufficient to maintain the oil during extra-ction completely liquid.

'I'he apparatus shown and described is especial- 1y suited for extracting hydrocarbon oils with methyl acetate. While I have thus specifically described my invention and cited an example to illustrate it, the same is not to be construed as limiting the invention, and only such limitations should be imposed as are indicated in the appended claims. f

I claim:

1. The method of producing a lubricating oil of high viscosity index from a lubricating oil fraction containing hydrocarbons of both high and low viscosity index which comprises mixing and agitating the lubricating oil fraction with methyl acetate at about normal room temperature, allowing the mixture to remain undisturbed to effect stratification, drawing oi the supernatant layer of treated oil and a relatively small amount of methyl acetate and separating said methyl acetate from the treated oil by distillation.

2. The continuous method of refining mineral oil containing hydrocarbons of both high and low viscosity index with methyl acetate to produce lubricating oil of a high viscosity index, low in sulphur and Conradson carbon content and resistant to oxidation which comprises alternately mixing together and then separating flowing bodies of the oil and the methyl acetate at about normal room temperature, the relatively saturated methyl acetate coming into contact with relatively fresh oi1 while the relatively finished oil comes into contact With fresh methyl acetate, and maintaining the bodies of oil and methyl acetate at a temperature of about 70 F. during the treatment.

3. The continuous method of refining mineral oil containing hydrocarbons of both high and low viscosity index with methyl acetate to produce lubricating oil of a high viscosity index, low in sulphur and Conradson carbon content and resistant to oxidation which comprises alternately mixing together and then separating flowing bodies of the oil and the methyl acetate, the relatively saturated acetate coming into contact with relatively fresh oil while the relatively finished oil comes into contact with fresh acetate, and maintaining the bodies of the oil and methyl acetate at about normal room temperature, while the relatively finished oil comes into contact with fresh methyl acetate, forming one portion of liquid composed of methyl acetate and dissolved material extracted from the oil and another portion composed of rened oil and a relatively small amount of methyl acetate, separately heating said liquid portions to a temperature at which the methyl acetate is vaporized, condensing the evolved vapors of methyl acetate, separately cooling the remaining treated oil and extract, and returning the separated condensed methyl acetate for extracting fresh oil.

4. The process of preparing a lubricating oil of high viscosity index from a lubricating oil fraction containing hydrocarbons of both high and low viscosity index by extraction with methyl acetate which comprises alternately mixing together and then separating flowing bodies of the lubricating oil fraction and methyl acetate at about normal room temperature, the relatively saturated methyl acetate coming into contact with relatively fresh oil while the relatively iinished oil comes into contact with fresh solvent methyl acetate.

5. The process of preparing lubricating oil of high viscosity index from a lubricating oil fraction containing hydrocarbons of both high and low viscosity index by solvent extraction which comprises mixing and agitating said fraction with a solvent liquid comprising methyl acetate, while maintaining the mixture at about normal room temperature forming a dissolved phase comprising low viscosity index constituents of the oil `dissolved in methyl acetate and an undissolved phase comprising high viscosity index constituents of the oil mixed with a relatively small amount of methyl acetate, separating the two phases, and removing the solvent liquid therefrom.

LOUIS A. CLARKE. 

